1. Field of the Invention
This invention relates to an optical information recording apparatus, in particular to a control circuit for controlling the start and interruption of its recording operation.
2. Description of the Related Arts
Devices for optically recording information on a recording medium, for example a video-disk, are known in the art. These are devices, for which a disk-shaped information carrier (hereinbelow abbreviated a disk), on which a photosensitive substance is applied or deposited by evaporation, is irradiated with a light beam (hereinbelow abbreviated by a light spot) coming from a laser light source. Information is recorded in the form of variations in optical characteristics due to melting and vaporization of the part of the substance irradiated with the light spot or to variations in the light reflection or transmission coefficient of that part by modulating the light output intensity with signals to be recorded; and the information thus recorded is reproduced by detecting the variations in optical characteristics. On the disk guide grooves (hereinbelow called guide tracks), which can be optically detected, are cut in advance in order to obtain high density recording tracks or to remove deviations of the trace due to the excentricity of the disk. The recording and reproduction is effected by focussing the light spot on these guide tracks and by bringing it under tracking control so that it follows the guide tracks.
FIG. 1 is a scheme illustrating an example of the disk. In the figure, for the sake of simplicity of explanation, only two concentric circular tracks 2 and 3 adjacent to each other are shown. On the disk 1 groove-shaped guide tracks are cut during fabrication. Address signals 4 for identifying each of the guide tracks are recorded in the hatched areas. A recording positioning mark 5 is formed in the form of a pit. This positioning mark is also used for a rotational synchronization signal of a disk drive motor 6.
FIG. 2 is a diagram showing an example of the optical information recording apparatus. In the apparatus shown in the figure, when an input signal is to be recorded, at first the number of tracks where the signal is to be recorded and a command signal for beginning the recording are inputted by a system control 29 consisting of a microcomputer, etc. to a recording gate circuit 28. Then, the recording positioning mark 5 constituted by the pit is detected by a photosensor 7 and the signal thus obtained is inputted to the recording gate circuit 28 after having been shaped in a waveform shaping circuit 27. The recording gate circuit 28 outputs a high level signal during a period of time corresponding to the number of tracks specified by the system control 29, in response to a recording positioning mark detecting signal coming from the waveform shaping circuit 27 and a recording start command signal coming from the system control circuit 29. A laser driving circuit 30 modulates the output of a laser diode 9 in intensity according to an input signal 8 when the level of the output of the recording gate circuit 28 is high.
The light beam generated by the laser diode 9 is transformed into a parallel light beam by means of a focussing lens 10. Further, since the semiconductor laser light beam has an elliptic cross-section, it is corrected to a light beam having an approximately circular light beam by means of a concave cylindrical lens 11 and a convex cylindrical lens 12. The corrected light beam is injected through a polarizing beam splitter 13 and a 1/4-wavelength plate 14 to an objective 16 mounted on an actuator 15. Then the light beam focussed by the objective 16 irradiates the surface of the photosensitive substance on a guide track of the disk 1 and performs the recording on the disk either by melting and vaporizing the part irradiated with the light beam or by varying the reflection or transmission coefficient of that part of the track. Light reflected by the disk 1 passes again through the objective 16 and the 1/4-wavelength plate 14 and is led to a convex lens 17 by the polarizing beam splitter 13. Then it is divided into 2 parts by a mirror 18, one of which is directed to a 2 -division photodiode 19 for the tracking error detection and the other of which is directed to a 2-division photodiode 22 for the focussing error detection. The output of the photodiode 19 is inputted to a differential amplifier 20 and used for detecting the deviation of the light spot from the guide track by detecting unbalance of the light reflected or diffracted by the disk by means of the differential amplifier 20. The lens 16 is driven in the direction perpendicular to the guide track through a tracking control circuit 21 by an actuator 15 so that this deviation detection output becomes zero, such that the light spot is controlled so as to follow the guide track. The output of the photodiode 22 is inputted to the differential amplifier 23, which detects the distance between the objective 16 and the disk 1. The output of the differential amplifier 23 drive the lens 16 in the direction perpendicular to the disk 1 by means of the actuator 15 through the focussing control circuit 24, controlling its position so that the light spot diameter on the surface of the disk 1 is approximately 1 .mu.m. Further, the output of the photodiode 22 is also inputted to an amplifier 25, where the recorded signals are reproduced, and the address signal 4 recorded in advance on the disk 1 is demodulated in an address demodulation circuit 26. This address signal is utilized for knowing on which track the recording is actually performed or for counting the number of tracks, on which recording has been already effected.
FIG. 3 is a block diagram showing a concrete construction of the recording gate circuit 28. The recording gate circuit 28 consists of a register 31, a down counter 32, a zero detection circuit 33 and a recording timing control circuit 34. In the case where input signals are recorded, the value (N+1) obtained by adding 1 to the difference N (integer) between the number of the first track at which recording should be begun and the number of the last track at which the recording should be terminated, i.e. the number of tracks on which the recording should be performed is preset in the register 31 by means of the system control 29. The data of this number of tracks are inputted in the DATA terminal in synchronism with the clock pulses to the CLK terminal.
The working mode of the circuit indicated in FIG. 3 will be explained below, referring to FIG. 4. At first an REC pulse b, which is a command signal for starting the recording, is outputted by the system control 29. Upon receiving the REC pulse b, the down counter 32 is loaded with the data of the number of tracks to be recorded, which has been preset in the register 31. The down counter 32 decreases the data of the number of tracks, with which it is loaded, by 1 every time a positioning mark detection signal a (hereinbelow called MARK pulse) coming from the waveform shaping circuit 27 arrives. The recording timing control circuit 34 detects the first MARK pulse, after the REC pulse has been inputted, and then outputs a recording gate signal d of high level. When the level of the recording gate signal d becomes high, the laser driving circuit 30 is activated and the recording on the disk 1 is started according to the input signal 8. When the recording proceeds so far that the number of tracks, with which the down counter 32 is loaded, decreases to zero, the zero detection circuit 33 detects the zero count and outputs a zero detection pulse c. When this zero detection pulse c is inputted, the recording timing control circuit 34 makes the level of the recording gate signal low and deactivates the laser driving circuit 30 so that the recording is terminated.
In much a recording apparatus, in the case where it was desired to interrupt the recording in the course of a recording on several successive tracks, heretofore, since the recording was interrupted at the same time as the input of an interruption signal from the system control 29, sometimes the track on which recording is in mid course is not recorded in whole. This gives rise to the problem that, when the track, for which the recording has been interrupted in mid course, is subsequently played, in a case of the video-disk, reproduced images become unstable and, in the case of a digital recording disk, reproduced data becomes erroneous.